Amyotrophic lateral sclerosis (ALS) is a fatal, adult-onset neuromuscular disorder characterized by the progressive loss of motor neurons in the spinal cord and brain. There is no adequate therapeutic for ALS, and patients typically die within 5 years of disease onset1. microRNAs are a promising new avenue for disease research. microRNAs are short single-stranded RNA molecules capable of regulating large numbers of mRNAs. microRNAs are dysregulated in a variety of diseases and have proven themselves to be viable therapeutic targets20,21. By comparing microRNAs in the spinal cords of our ALS rodent model to age-matched controls, we discovered a robust and significant increase in specific microRNAs. Of particular interest is miR-155, a microRNA expressed by immune cells and known to be involved in inflammation and immunity27. We have since confirmed this microRNA to also be significantly upregulated in ALS patient autopsy spinal cord tissue. We will study the role of this inflammatory mediating microRNA in our ALS rodent model in order to elucidate its role in neurodegeneration and to test its intervention potential. In Aim 1, we will collect time course data and perform in situ hybridization in order to learn when the expression levels of our microRNA of interest begin to change and in order to determine which cells in the spinal cord dynamically modulate their miR-155 expression during disease. Next, in Aim 2, we will determine the importance of miR-155 during neurodegenerative disease and its impact on disease pathways. We are currently breeding miR-155 knockout animals into our ALS mouse line. We will compare the mice in their age of disease onset and overall longevity. In order to link mechanism to phenotype, we will complement these studies with immunohistological and molecular assays that will evaluate changes in neuroinflammatory pathways. Finally, in Aim 3, we will knock down miR-155 with antisense oligonucleotides delivered directly into the cerebral spinal fluid with osmotic pump technology. In addition to developing a novel knockdown technique for microRNAs, this work will also allow us to modulate our microRNA both temporally and spatially - furthering our mechanistic insight (peripheral vs. central effect) while also testig a potential therapeutic. If successful, the proposed experiments will expand our understanding of the role of microRNAs in neuroinflammation and may also help inform the development of a novel ALS therapeutic.